Mobile communication device with subscriber identity module

ABSTRACT

The present invention relates to a mobile communication device for communicating with a cellular network by means of a serving base node, the mobile communication device further being connected to a subscriber identity module, the mobile communication device being configured to operate in a power optimization mode wherein the power optimization mode comprises extended paging periods, and the mobile communication device is further configured to set up a communication context with the base node using authentication means of the subscriber identity module, wherein the mobile communication device is further configured, in case of detection of a removal of the subscriber identity module and when the power optimization mode is activated: to send an removal alert message to the serving base node by means of said communication context, afterwards to terminate the communication context.

FIELD OF THE INVENTION

The present invention relates to a mobile communication device with asubscriber identity module.

The invention also pertains to method for operating said mobilecommunication device. Further the invention relates to a cellularnetwork configured to communicate with a mobile communication device.

BACKGROUND OF THE INVENTION

In the field of wireless cellular communication it is known that eachmobile communication device is operated with a subscriber identitymodule, in particular a SIM card or UICC. The subscriber identity moduleenables to authenticate towards the cellular network the one mobilecommunication device where it is connected with.

To assure that at one time only one mobile communication device incombination with the same subscriber identity module is authenticatedtowards the cellular network, it is known, that the mobile communicationdevice needs to ensure that the subscriber identity module has not beenremoved during a communication session. This is done by sending witheach paging a status command to the subscriber identity module. Shouldthis presence detection fail, the mobile communication device has toterminate the communication session immediately. By this means it isassured that a subscriber identity module is not used by two activemobile communication devices on the cellular network.

In the field of wireless cellular communication a new category ofdevices is introduced in particular covered by new technologyspecification of long term evolution (LTE), which are the so-calledmachine-type communication (MTC) devices. Such MTC devices furthercomprise so-called low cost devices, which are supposed to operate inLTE networks only in a limited way, and hence less equipped withprocessors and other hardware resources than a full-featured LTEhandset.

Those MTC devices are in particular characterized by the fact that theyare operated with a battery with an expected lifetime without rechargingwhich is far larger than that of mobile handsets. This is in particularachieved by considering that they are rarely contacted and practicallyoperated stationary, hence a lot of operations used for regularcommunication measures with the cellular network resp. the base nodewhere the mobile communication device is camping on—hereinafter calledthe serving base node—can be omitted or at least drastically reduced.

One of these operations is the DRX cycle which indicates the frequencyfor listening to paging messages from the serving base node. For suchmachine-type communication devices it is foreseen in particular a lowpower mode, where at least the DRX cycle is massively enlarged. Instandardization document ETSI TS 26.304 Rel. 13.0.0 it is in particularsuggested to allow DRX resp. extended DRX (eDRX) cycles with PagingHyperframes (PH) leading to cycles of 3 to 24 hours. This is fullysufficient for a machine-type communication device, which e.g. once aday sends metering data to a remote server. Further the new Power SavingMode (PSM) foresees to leave the mobile communication device asleep fora defined time period longer than e.g. a day, introduced instandardization document ETSI TS 24.301 Rel. 12.5.0.

However, with the increase of the DRX cycle it means at the same timethat the frequency of detection of the presence of the subscriberidentity module is increased to those values as well. This is inparticular a problem, as for machine-type communication devicestypically the SIMs/UICCs are accessible without removing the battery,unlike it is typically the case for mobile handsets.

In effect there is with recent developments of MTC devices the risk of asecurity leak in that sense, that more than one mobile communicationdevice could without detection be registered in a cellular network withthe same subscriber identity modules at the same time.

It is therefore the goal of present invention to provide a solutionwhere this shortcoming of the recent developments is omitted and thatthe mobile communication device and the cellular network can react incase of removal of a subscriber identity module from the mobilecommunication device.

Further alternative and advantageous solutions would, accordingly, bedesirable in the art.

SUMMARY OF THE INVENTION

For this it is according to a first aspect of the invention suggested amobile communication device according to claim 1. It is furthersuggested according to a second aspect of the invention a method tooperate a mobile communication device according to claim 7.

According to the first aspect of the invention it is proposed a mobilecommunication device for communicating with a cellular network by meansof a serving base node, the mobile communication device further beingconnected to a subscriber identity module, the mobile communicationdevice being configured to operate in a power optimization mode whereinthe power optimization mode comprises extended paging periods, and themobile communication device is further configured to set up acommunication context with the base node using authentication means ofthe subscriber identity module, wherein the mobile communication deviceis further configured, in case of detection of a removal of thesubscriber identity module and when the power optimization mode isactivated:

-   -   to send an removal alert message to the serving base node by        means of said communication context,    -   afterwards to terminate the communication context.

The invention relates to a mobile communication device operating in acellular network for wireless communication. The mobile communicationdevice is generally any kind of device comprising at least acommunication unit and an antenna for accessing the wireless airinterface to the serving base node. The serving base node is one of aplurality of base nodes belonging to the cellular network. It is thebase node the mobile communication device is camping on.

The base node is the entry point of the cellular network to the airinterface. Depending upon the supported technology, like 2G (GSM, GPRS,EDGE), 3G (UMTS, HSPA), 4G (LTE, LTE-Catx, LTE-M) the base node isimplemented in particular as a base station (BS), nodeB, eNodeB.

The mobile communication device further comprises a subscriber identitymodule. This is a secure unit, which holds in its secured memory allnecessary credentials for authenticating at the cellular network uponregistration. The subscriber identity module is preferably provided bythe network operator. It is put into the mobile communication device,which provides a SIM-card holder and with a connected subscriberidentity module the mobile communication device is enabled to registerat the cellular network. Typical embodiments of the subscriber identitymodule are a SIM-card or UICC which are typically removable, as well asan eUICC which is typically, but not necessarily soldered to the mobilecommunication device. Other embodiments are further thinkable, e.g. inconjunction with another secure card, like a banking card, which isremovable and holds the credentials.

The mobile communication device is further configured to operate in apower optimization mode. This is in particular a mode which allows themobile communication device to operate with the cellular network in away which requires less signalling between the mobile communicationdevice and the serving base node.

In particular stationary mobile communication devices, in particularmachine-type communication (MTC) devices are configured to operate insuch a power optimization mode. One of those power optimization modes isthe standardized Power Saving Mode (PSM). Such Power Saving Mode ispreferably designed to enhance the periods until a mobile communicationdevice is expected to be paged. Such enhancement is more in the area ofdays rather than minutes. The concept is known as enhanced discontinuousreception (eDRX).

When a mobile communication device is registered at a base node itregularly carries out paging operations, which are mainly for checkingif income messages or calls are present. In case of an active powersaving mode such pagings are carried out only rarely, that is the pagingperiod is massively expanded. By this the power consumption for thepaging operation is omitted and such the battery lifetime is remarkablyextended.

The mobile communication device is according to the invention configuredto set up a communication context. Such communication context is inparticular a Packet Data Protocol (PDP) context or an active EvolvedPacket System (EPS) bearer context. Such context is envisaged to allowpacket data exchange between mobile communication device and thecellular network, and allows to be resumed after a certain amount oftime.

The setting up of the communication context is preferably carried out byan attach command. With that a data context session is established, andthe mobile communication device gets in particular assigned an IPaddress.

Additionally the mobile communication device is further configured tocheck with each paging operation if the subscriber identity module isstill connected to the mobile communication device.

Nonetheless the mobile communication device further comprises additionalmeans to asynchronously detect if the subscriber identity module wasremoved.

It is in particular proposed to detect the removal of the subscriberidentity module by means of at least one of

-   -   a mechanical removal indicator pin, or    -   a polling mechanism.

The removal indicator pin is a physical interrupt, known as CCIN, whichindicates a physical removal from the SIM card holder of the mobilecommunication device.

With a polling mechanism it is possible to actively check for theavailability of the subscriber identity module asynchronously to thepaging cycle. Preferably this type of polling is carried out prior toeach data transmission, when a communication context is established.

Once the mobile communication device detects the removal of thesubscriber identity module, it is configured to send a removal alertmessage to the serving base node. This message is preferably sent byusing the still existing communication context. It is the only allowedmessage transmission with a knowingly removed subscriber identitymodule.

It is further proposed that the removal alert message comprises at leastan indication identifying the subscriber identity module or anyidentification of the certain mobile communication device.

With such a removal alert message the cellular network is informed aboutthe removed subscriber identity module. This is advantageous as it cantake appropriate measures in order to disallow a further registration ofanother mobile communication device by using the removed subscriberidentity module. Without the removal alert message it would not beinformed about this situation.

Preferably the removal alert message comprises identifying informationunique for the subscriber identity module or the mobile communicationdevice. In particular the IMEI resp. the IMSI would be appropriate forthis purpose. In conjunction with further systems relating to networkbased device management also other identifiers are foreseen to be used.

Consequently the mobile communication device further terminates thecommunication context after the removal alert message is sent. This ispreferably achieved by a context close command. This makes sure that nofurther communication is possible with the mobile communication device,as long as no eligible subscriber identity module is connected.

Further all authentication data resulting from the subscriberauthentication at the cellular network are removed from the mobilecommunication device. Preferably also from the cellular network datarelating to the authentication session of the subscriber identity moduleare removed. With that it is clear that the subscriber identity moduletogether with this mobile communication device is not authenticatedanymore. It hence requires a new registration at the cellular network ifwith a new or the same mobile communication device. It is up to thecellular network, if the subscriber identity module is even blocked ormarked in response to reception of a removal alert message. Hence suchfraud is successfully prevented on both ends of the air interface, andthe opened security leak through the eDRX introduction is closed.

It is further in an advanced embodiment of the invention proposed toterminate the communication context as soon as an acknowledgementmessage from the serving base node is received.

This advantageous embodiment is dedicated to assure that the cellularnetwork receives the removal alert message. Therefore the mobilecommunication device first expects an acknowledgement message indicatingif the removal alert message was successfully received.

When the removal alert message was received, the mobile communicationdevice knows that the cellular network is informed about the situationof the removed subscriber identity module. In response it can thereforeclose down the communication context, in particular the PDP context. Bythis any continued communication with the cellular network is prevented.So this advantageously assures that the removal alert message is thelast message that was submitted by the mobile communication device withthe existing communication context, but without connected subscriberidentity module.

If the removal alert acknowledgment message was not received, then it isproposed in another preferred embodiment for the mobile communicationdevice to resend the removal alert message to the serving base node incase the acknowledgement message is not received within a predeterminedresponse time.

With this embodiment the mobile communication device takes care aboutthat the cellular network gets reliably informed about the removal ofthe subscriber identity module. This applies in particular when thecellular network does not send a response at all, or a responseindicating that the removal alert message was not successfully received.The latter is in particular the case when the removal alert messagecould not be decoded, or any sanity check might fail. Further when theindication identifying the subscriber identity module is inappropriatee.g. not known to the cellular network is preferably a reason to send anot-acknowledge message.

Depending upon the content of the response message the mobilecommunication device decides to make a retry by sending another removalalert message or to continue with the next operation, in particularending of the communication context.

When the mobile communication device decides to do a retry, it is inparticular proposed to carry out the resend operation with a highersignal strength than the previous send operation.

With this embodiment the mobile communication device is configured toovercome transmission issues from the first removal alert messagetransmission. This increases the likelihood that the cellular networkreceives the removal alert message.

Advantageously the mobile communication device further maintains acounter indicating the number of retries. So it is assured that after apredetermined amount of resending operations without an acknowledgementmessage the mobile communication device bails out to continue.

According to the second aspect of present invention it is suggested amethod to operate a mobile communication device configured tocommunicate with a cellular network by means of a serving base node,further being connected to a subscriber identity module, and the mobilecommunication device being configured to operate in a power optimizationmode wherein the power optimization mode comprises extended pagingperiods, and the mobile communication device is further configured toset up a communication context with the base node using authenticationmeans of the subscriber identity module,

the method comprising, in case of detection of a removal of thesubscriber identity module and when the power optimization mode isactivated, the steps of:

-   -   sending an removal alert message to the serving base node by        means of said communication context,    -   afterwards terminating the communication context.

The second aspect shares the advantages of the first aspect.

In a third aspect it is proposed a cellular network, comprising aplurality of base nodes, configured to communicate with at least onemobile communication device comprising a subscriber identity module,wherein the cellular network is further configured, upon reception of anremoval alert message at a base node, to discard authentication data ofthe subscriber identity module, where the removal alert message isreferring to.

This aspect of the invention relates to the cellular network. Accordingto that the cellular network is prepared to receive a removal alertmessage from a mobile communication device, in particular a mobilecommunication device. according to the first aspect of the presentinvention.

When the cellular network, in particular via a base node of it, receivesthe removal alert message, it is preferably first decoded.

At what component of the cellular network this is carried out, dependsupon the architecture of the cellular network, including the supportedtechnology standard.

The base node or a respective unit responsible for the spatial region ofthe base node, e.g. the Mobility Management Entity (MME) would be a goodplace, as it is very likely that a subscriber identity module removedfrom one mobile communication device would be used in another mobilecommunication device situated in proximity of the first mobilecommunication device. Hence, the same tracking area or region isresponsible for this.

After decoding the removal alert message the cellular network preferablychecks the content of the message and if it is accurately understood.E.g. if the subscriber identity module ID comprised in the removal alertmessage is unknown, then it cannot be handled properly.

Preferably the removal alert message makes use of already existingmessages and channels that are already in place for control signalsbetween mobile communication device and the cellular network.

In another preferred embodiment of this aspect of the invention it isfurther proposed to send upon reception of the removal alert message anacknowledgment message to the mobile communication device indicating ifthe removal alert message was successfully received.

According to this embodiment the outcome of the checks for the receivedremoval alert message at the cellular network is preferably reportedback to the sending mobile communication device by way of a responsemessage. If the response is positive, the response message resp. theacknowledgment message indicates that the reception of the removal alertmessage was successful.

If not, preferably the cellular network sends another response messageresp. not-acknowledgment message indicating that the reception of theinitial message was not successful. In particular when the removal alertmessage was not understandable by the cellular network as that type ofmessage preferably any type of response indicating this fact isadvantageous.

Preferably the mobile communication device is configured to reactproperly, so that it either continues its process or tries again to sendthe removal alert message.

In any case, when the removal alert message is successfully received atthe cellular network, then the transmitted information are taken intoaccount in order to prevent fraudulent registration with the removedsubscriber identity module.

Preferably the communication context of the first mobile communicationdevice is terminated, in particular right after sending a responsemessage.

Any data related to the communication context, in particularauthentication data are deleted, in the base node and/or the MME.

Preferably the cellular network may decide that any authentication datarelating to the subscriber identity module get marked as blocked or atleast marked as potentially illegally used. This is in particularapplicable as long as the original mobile communication device togetherwith the original subscriber identity module tries to register in thecellular network. Alternatively it is preferable that the subscriberidentity module together with another mobile communication device is notable to register in the cellular network.

Such registration would in that case be prevented. This option would inparticular lead to a temporary blocking.

So this aspect of the invention advantageously closes the last gap, sothat both on mobile communication device and on cellular network sideeverything is done, to attack said security leak.

As it is shown this invention advantageously solves the problem with thedepicted security leak and provides a reliable approach to avoid withoutimpacting of the normal operation the use of a subscriber identitymodule with a second mobile communication device, while a first mobilecommunication device is still in a communication context.

BRIEF DESCRIPTION OF THE DRAWINGS

The following description and the annexed drawings set forth in detailcertain illustrative aspects and are indicative of but a few of thevarious ways in which the principles of the embodiments may be employed.Characteristics and advantages of the present invention will appear whenreading the following description and annexed drawings of advantageousembodiments given as illustrative but not restrictive examples.

FIG. 1 represents a mobile communication device of the type to which thepresent invention is applied to as an embodiment in conjunction with acellular network;

FIG. 2 shows a flow chart indicating a process flow according to apreferred embodiment of the invention;

FIG. 3 represents a flow chart indicating a process flow according toanother preferred embodiment of the invention;

FIG. 4 shows a subscriber identity module connected with a mobilecommunication device according to an embodiment of the invention;

FIG. 5 represents a sequence diagram indicating the messaging between amobile communication device and a cellular network according toembodiments of the current invention.

FIG. 1 schematically shows a mobile communication device 1 of the typeto which the present invention is applied as an embodiment. It isequipped with all components required for communicating with a base node3 of a cellular network 2.

Such components are in particular an antenna 5 and a subscriber identitymodule 4, in particular a SIM card or an UICC. This subscriber identitymodule 4 is in particular removable from the mobile communication device1. The mobile communication device 1 is in the shown embodiment amachine-type communication device, in particular a metering device. Thisis typically installed that way that is not movable, resp. operatedstationary.

Such machine-type communication (MTC) devices 1 have the peculiaritythat they only rarely send measured data, like electricity consumption,to a remote central server. They are practically never called fromoutside, and if so, they do not have means to take the call. Hence,there is for such a mobile communication device neither a need to checkfor neighbour cells regularly nor for paging in order to determine anincoming call.

On the other hand such a machine-type communication devices ispreferably operated with a battery. Hence the power consumption is ofessence for the maintenance-free lifetime of the mobile communicationdevice.

For such scenarios concepts like Power Saving Mode (PSM) are foreseen.According to those concepts, at least the DRX cycle is extremelyenhanced, consequently leading to the eDRX with a duration of many hoursor even days. It takes both the base node 3 resp. cellular network 2 andthe mobile communication device to support this mode. In the followingit is assumed, that both serving base node 3 and the mobilecommunication device 1 in question support PSM or a similar poweroptimization mode, comprising enhanced paging cycles.

As it can be seen, for such mobile communication devices the subscriberidentity module 4 is not necessarily located below the battery, as it isthe case for most of the mobile handsets. That implies that during a setup communication context of a mobile communication device, thesubscriber identity module 4 may be removable without powering down themobile communication device.

For that purpose the invention is foreseen.

FIG. 2 shows a flow chart of an advantageous first embodiment of theinventive method. It starts in step S1 with a mobile communicationdevice 1 camping on a base node 3. Preferably it is a base nodesupporting a power optimization mode. Preferably the mobilecommunication device registered before on this base node. As part ofthis, it authenticated at the cellular network 2 with the credentialsstored in the subscriber identity module 4.

After a while the mobile communication device automatically or drivenfrom outside—either through manual input or cellular networksignalling—activates the power optimization mode (step S2). This modecomprises at least an increase of paging cycles resp. eDRX. Other powerintensive operations might be switched off or reduced in parallel, likemobility functions etc.

In step S3 then the mobile communication device establishes with thecellular network a communication context. This happens in particular byan attach command to the cellular network, and/or a context activation.With doing that the mobile communication device is in the situation toexchange data with the cellular network. It has an IP address assignedand can send and receive data packets to/from the cellular network.Typically it is called a data session setup.

This step is not mandatorily carried out after switching to the lowpower mode. On the other hand it is advantageous to do so, as for theestablished communication context the signalling conditions do notchange afterwards. In the following the mobile communication devicemight send or receive data to/from the cellular network by means of thecommunication context, as indicated by step S4.

In step S5 it is then checked if the SIM (resp. UICC) is still connectedwith the mobile communication device. This is happening in particular byan interrupt, like CCIN or by polling. The polling is runningasynchronous to the paging procedure, different from the non-PSMstandard compliant mobile communication devices. Preferably theavailability of the subscriber identity module is polled prior to eachdata transmission.

Should the SIM still be connected, the operation continues with step S4.A waiting period or other operations may happen in the meantime.

Otherwise a situation is detected where the mobile communication deviceis not in the position to use the cellular network anymore, as thesubscriber identity module has been removed.

Hence the process flow branches to step S6. During this step a removalalert message is sent to the cellular network, resp. the base node. Thisis done in order to inform the cellular network about a potential fraudaction.

Preferably the cellular network takes appropriate steps as indicatedwith the third aspect of the invention. For that the removal alertmessage in particular comprises an indication for identifying theremoved SIM card, in particular IMSI or MS-ISDN.

It is a unique situation that a mobile communication device knowinglywithout a connected subscriber identity module sends data signals to thecellular network. This is only possible by means of the already setupcommunication context. This is the proof that the mobile communicationdevice was just recent eligible to access the cellular network. Hence itis not necessarily important if the removal alert message is sent bymeans of the communication context, but at least while the communicationcontext is still active.

After successfully sending of the removal alert message, the mobilecommunication device directly terminates in step S7 the communicationcontext. With that it is assured that this mobile communication devicewill not send any other data in the current status of an activecommunication context but without connected subscriber identity module.

FIG. 3 shows a variant of the previously shown flow chart, here with amore detailed view at the end of the process. The common operation stepswith previous FIG. 2 have the same reference number. So the process isstarted with steps S6, which follows the detection of the removedsubscriber identity module in FIG. 2.

After the removal alert message is sent, the mobile communication devicechecks in step S11 for a response from the serving base node. There aredifferent possibilities to respond. One is no response at all, anotherone is an acknowledgment response message, and further there is anon-acknowledgement response message.

For receiving an acknowledgement response message (ACK) it is foreseen apreconfigured time for a response. If no response arrives in this timer,then the process flow branches along the no-path to step S12.

If a message is received from the cellular network, it is analysed if itcomprises an acknowledgement or a non-acknowledgement. In case of anacknowledgment, the process flow branches to step S7.

Otherwise the process flow branches to step S12. Here it is suggested toincrease signal strength. This is in particular advantageous when noresponse was received. But also a non-acknowledgment response messagemight be an indicator for bad signalling reception at the base node.When this branch is taken, preferably a counter is incremented. Withthis counter it is measured how often it was tried to resend the removalalert message in step S6.

Hence, when the process flow returns to step S11 for decision if theremoval alert message was understood0 well, also the counter is takeninto account. If the counter is higher than a predeterminedthreshold—something in the medium one-digit range was foundreasonable—then the process flow branches to step S7, no matter if anacknowledgment was received in time and/or what content it provided.

In step S7 then the mobile communication device terminated thecommunication context and stops working until an activated and notblocked subscriber identity module is connected again.

FIG. 4 shows schematically the connection of a subscriber identitymodule 4 with a mobile communication module 1. It typically is connectedby a SIM card holder 5. This SIM card holder comprises a limited numberof connectors 6 for accessing the pins of the subscriber identity module4. Each pin/connector has its special task. One pin is assigned to theinterrupt connector CCIN. This is a hardware interrupt. When thesubscriber identity module 4 is removed, then the CCIN is opened and aninterrupt is triggered. This interrupt is detected within the mobilecommunication device 1 and triggers the process flow according to theinvention, as shown in the following FIG. 5.

FIG. 5 shows for a preferred embodiment of the invention a message flowbetween the mobile communication device 1 and the cellular network 2, inparticular represented by a base node 3. In message M1 the mobilecommunication device detects the removal of the subscriber identitymodule, in particular by the interrupt pin CCIN.

In response, the mobile communication device sends a message M2 to thecellular network 2, resp. the base node 3. This message M2 is calledUICC_REMOVAL_ALERT, indicating the removal of the subscriber identitymodule.

In this case the UICC_REMOVAL_ALERT message further comprises the IMSIfor indicating the removed subscriber identity module.

In the following the mobile communication device has activated step S20for waiting for a response from the cellular network. Should no responsecome in a given time range, then the mobile communication devicecontinues working. Alternatively another UICC_REMOVAL_ALERT is sent bythe mobile communication device, preferably with higher signal strength.

In the shown case, the cellular network sends a response message M3,called UICC_ALERT_RESPONSE. This is to confirm reception of theUICC_REMOVAL_ALERT message, resp. any alert message. In this embodimentthe response message further provides an indicator ACK if theUICC_REMOVAL_ALERT message is acknowledged, which means it is understoodand processed. In the simplest form, the ACK parameter is a simplebinary argument indicating if the removal alert message M2 was wellreceived or not.

If the indicator is ACK=true, then the mobile communication devicecontinues with message M4, which comprises the termination of thecommunication context.

After finishing this process flow, all the relevant steps for facing theunauthorized removal of the subscriber identity module.

On the side of the cellular network preferably additional steps aretaken to end the registration resp. context of the mobile communicationdevice 1 in conjunction with the removed subscriber identity module 4.

In the above detailed description, reference is made to the accompanyingdrawings that show, by way of illustration, specific embodiments inwhich the invention may be practiced. These embodiments are described insufficient detail to enable those skilled in the art to practice theinvention. It is to be understood that the various embodiments of theinvention, although different, are not necessarily mutually exclusive.For example, a particular feature, structure, or characteristicdescribed herein in connection with one embodiment may be implementedwithin other embodiments without departing from the scope of theinvention. In addition, it is to be understood that the location orarrangement of individual elements within each disclosed embodiment maybe modified without departing from the scope of the invention. The abovedetailed description is, therefore, not to be taken in a limiting sense,and the scope of the present invention is defined only by the appendedclaims, appropriately interpreted, along with the full range ofequivalents to which the claims are entitled.

The invention claimed is:
 1. A mobile communication device forcommunicating with a cellular network by means of a serving base node,the mobile communication device further being connected to a subscriberidentity module having authentication credentials, the mobilecommunication device being configured to operate in a power optimizationmode wherein the power optimization mode comprises extended pagingperiods, and the mobile communication device is further configured toset up a communication context with the base node using theauthentication credentials of the subscriber identity module, whereinthe mobile communication device is further configured, in response todetection of a removal of the subscriber identity module while operatingin the power optimization mode: to send a removal alert message to theserving base node by means of said communication context, and toterminate the communication context subsequently to the sending of theremoval alert message.
 2. The mobile communication device according toclaim 1, wherein the removal alert message comprises at least anindication identifying the subscriber identity module or anyidentification of the mobile communication device.
 3. The mobilecommunication device according to claim 1, further configured toterminate the communication context as soon as an acknowledgementmessage from the serving base node is received.
 4. The mobilecommunication device according to claim 3, further configured to resendthe removal alert message to the serving base node in response to notreceiving the acknowledgement message within a predetermined responsetime.
 5. The mobile communication device according to claim 4, furtherconfigured to carry out the resend operation with a higher signalstrength than the previous send operation.
 6. The mobile communicationdevice according to claim 1, further configured to detect the removal ofthe subscriber identity module by means of at least one of a mechanicalremoval indicator pin, or a polling mechanism.
 7. A method to operate amobile communication device configured to communicate with a cellularnetwork by means of a serving base node, further being connected to asubscriber identity module having authentication credentials, and themobile communication device being configured to operate in a poweroptimization mode wherein the power optimization mode comprises extendedpaging periods and the mobile communication device being configured toset up a communication context with the base node using theauthentication credentials of the subscriber identity module, the methodcomprising, in response to detection of a removal of the subscriberidentity module while operating in the power optimization mode, thesteps of: sending a removal alert message to the serving base node bymeans of said communication context, terminating the communicationcontext subsequently to the sending of the removal alert message.
 8. Themethod according to claim 7, wherein the removal alert message comprisesat least an indication identifying the subscriber identity module. 9.The method according to claim 7, wherein the step of terminating of thecommunication context is carried out upon reception of anacknowledgement message from the serving base node.
 10. The methodaccording to claim 9, further comprising the step of resending theremoval alert message to the serving base node in response to notreceiving the acknowledgement message within a predetermined responsetime.
 11. The method according to claim 7, wherein the detection of theremoval of the subscriber identity module is carried out by means of atleast one of: a mechanical removal indicator pin, or a pollingmechanism.